This project examines the role(s) of the gram negative oral microorganism Cytophaga sp. in the initiation, development and progression of periodontal diseases. These bacteria are constituents of dental plaque and are strongly implicated in the pathogenesis of destructive periodontitis. A series of monoclonal antibodies have been developed with specificity for human oral isolates of Cytophaga sp. and the related species, Capnocytophaga. These antibodies are being used in continuing studies of attachment and aggregation of these bacteria and a clinical study of the role of these bacteria in human periodontal disease. Attachment of bacteria to the tooth surface or aggregation to previously attached bacteria represents the initial step in the periodontal disease process. An in vitro attachment assay has been developed for Cytophaga sp. bacteria to examine mechanisms of attachment and the role of serum and serum-derived factors in the attachment process. Clinical studies involve patients with well characterized stages of periodontal diseases who are studied prior to and during treatment. The presence of Cytophaga and Capnocytophaga sp., or of serum antibody to these bacteria, are examined at several times while therapy is accomplished. The goal of this project is to establish a relationship between these specific bacteria and the severity of a patient's periodontal disease.